The invention is directed to a two-roller machine, particularly a high-pressure roller press for pressure treatment of granular material with two oppositely rotatable rollers separated from one another by a nip and between which the granular material is drawn in and subjected to an interparticle comminution, having a product delivery shaft above the nip.
The invention is also directed to a method for the pressure comminution of granular material with such a two-roller machine.
During operation of the high-pressure roller press for compression or, respectively, for pressure comminution of granular material, the bulk material supplied to the nip is seized by the oppositely rotating rollers and is drawn into the nip by friction (friction within the bulk material and friction between the bulk material and the roller surface). The individual particles of the bulk material that is drawn in are thereby mutually crushed in a product bed, i.e. in a material fill compressed between the two roller surfaces given application of high pressure, so that one thereby refers to interparticle crushing (German Letters Patent 27 08 053 and corresponding U.S. Pat. No. 4,357,287). Agglomerates of comminuted bulk material are the product of this pressure treatment and can be subsequently loosened with little mechanical outlay.
A correspondingly high friction for the occurrence of a high-pressure interparticle comminution is dependent on the nature of the material to be comminuted (brittleness, grain structure, grain shape) and on the embodiment of the roller surface. In particular, the maximum grain size that can still be drawn in by the rollers is limited. Given roller surfaces implemented with high abrasion resistance, thus, the maximum charging grain should be smaller than the nip. Given normal execution of the roller surface, the delivered grain size should not exceed twice the value of the nip.
In order to meet this demand, EP-A-O 278 858 proposes that a crushing roller in which the entire bulk material is pre-comminuted precedes the high-pressure roller press. What is disadvantageous about this procedure is that all of the bulk material, i.e. the particles with adequately small grain size as well, are conducted through the crushing roll, as a result whereof the energy consumption of the overall process is unnecessarily increased and, further, that the machine outlay for the high-pressure comminution increases with the crushing roll as an independent machine.